Google plans to offer accounts to children under 13 years old for the first time, a move that will take the world’s largest Internet search provider into a controversial and operationally complex new market.

Accounts on Google services such as Gmail and YouTube are not officially offered to children, though there is little to stop them from logging on anonymously or posing as adults to sign up for accounts.

Now Google is trying to establish a new system that lets parents set up accounts for their kids, control how they use Google services and what information is collected about their offspring, according to a person familiar with the effort.

Earlier this year, Google was developing a child version of its online video site YouTube suited to tablet computers that would let parents control content, another person familiar with the company’s plans said.

Google and most other Internet companies tread carefully because of the Children’s Online Privacy Protection Act, or COPPA. The law imposes strict limits on how information about children under 13 is collected; it requires parents’ consent and tightly controls how that data can be used for advertising. (Companies are not liable if customers lie to them about user ages).

The company’s new effort is partly driven by the fact that some parents are already trying to sign their kids up to the company’s services. Google wants to make the process easier and compliant with the rules, the person said.

News of Google’s changes in this area has already caused concern among privacy advocates.

“Unless Google does this right it will threaten the privacy of millions of children and deny parents the ability to make meaningful decisions about who can collect information on their kids,” said Jeff Chester, executive director of the Center for Digital Democracy, an online privacy group.

Chester said The Center for Digital Democracy shared its concerns on Monday about Google’s new effort with the Federal Trade Commission, which writes COPPA rules and enforces them with state regulators.

The privacy group is also huddling with its legal team on Wednesday to create an action plan to monitor how Google rolls out its services for children and to make sure the system provides parents enough control over the privacy of their kids’ information, Mr. Chester added.